Project Summary Interventions are urgently needed to improve the delivery and impact of mental health services for persons with serious mental illnesses (SMI) in prison. Treatments addressing the symptoms of mental illness form a critical component of the continuum of services needed by prisoners with SMI. However, a growing body of literature shows that mental health treatments need to be combined with treatments that directly address criminogenic risk factors (i.e., those factors most closely associated with criminal activities). Despite their promising evidence, interventions that address criminogenic risk factors, such as Thinking for a Change (T4C), are not used with prisoners with SMI because of the neurocognitive and social impairments associated with SMI. This R34 involves a 2-phase pilot study that examines the effectiveness of a criminogenic intervention that incorporates a modified delivery system designed specifically to address the unique needs of persons with SMI in prison. Phase 1 consists of an open trial (n=16) in which we will finalize the T4C-SMI treatment manual. In Phase 2, we will conduct a small-scale RCT (n=60) to explore the potential effectiveness of T4C-SMI towards improving impulsivity, criminal attitudes, and interpersonal problem solving (treatment targets) and levels of aggression, and the amount of behavioral infractions and time spent in administrative segregation in prison (outcomes). Phase 2 will also examine whether the treatment targets for T4C-SMI mediate the intervention's impact on outcomes. Our long-term goal is to grow the evidence-base for interventions with the capacity to improve prison and community-reentry outcomes for persons with SMI. This R34 project will provide the data needed to implement a rigorous RCT in a future study and supports NIMH's mission to develop innovative interventions in mental health services.